Computer algorithms are used increasingly widely by police in the US and UK to scan crowds for known offenders. However, a security researcher in the US said he had discovered that common facial-recognition systems can be fooled by people wearing clown make-up.

Ian O’Neill, from Los Angeles, said he made the discovery when he tested multiple images of fans of the controversial hip-hop band Insane Clown Posse. Followers of the US duo, known as Juggalos, commonly copy the black-and-white facial designs of the singers Shaggy 2 Dope and Violent J.

Mr O’Neill tweeted: “I made a breakthrough. It turns out Juggalo makeup defeats facial-recognition successfully. If you want to avoid surveillance, become…

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